1. Field of the Invention
The present invention relates to a radio signal processing apparatus of a portable telephone, and in particular, to a radio signal processing apparatus which can share a cellular digital/analog compatible mode and a personal communication service mode.
2. Description of the Related Art
A personal communication service (PCS) represents a mobile communication service involving a walker and provides a radio service within a service area by processing a portion of regionally fixed subscriber lines by radio. A walker may be a person who is slowly walking with a portable communication device in a mobile communication service. Thus, a mobile communication service involving a walker refers to a mobile communication service capable of communication with persons travelling (e.g., walking) at a relatively low speed condition.
To use a portable telephone in a digital/analog compatible mode, a radio signal processing apparatus has been proposed as shown in FIG. 1. The digital/analog compatible mode is a new standard (IS-95; TR-45) in which an analog system is compatible with a digital system. The digital/analog compatible standard IS-95 specifies that a frequency bandwidth assigned to an analog cellular telephone can be used in a code division multiple access (CDMA) digital system. Therefore, the radio signal processing apparatus of FIG. 1 can be used in both a digital system and an analog system. The receiving and transmitting frequency ranges used in the radio signal processing apparatus are 868.5-893.5 MHz and 823.5-848.5 MHz, respectively.
Referring to FIG. 1, the radio signal processing apparatus of the digital/analog compatible portable telephone includes a digital/analog compatible converter 110, an intermediate frequency (IF) signal processor 112 and an antenna 114. The digital/analog compatible converter 110 transmits or receives a signal in tune with a frequency band of 800 MHz. The IF signal processor 112 generates an IF signal used in the radio processing apparatus of the digital/analog compatible portable telephone or processes a signal transmitted to or received from the digital/analog compatible converter 110. The digital/analog compatible converter 110 which is tuned with the frequency band of 800 MHz includes a duplexer 116, a digital/analog compatible receiving signal converter 150 having a low-noise amplifier (LNA) 118, a band pass filter (BPF) 120, a receiving mixer 122 and a multiplier 124, and a digital/analog compatible transmitting signal converter 152 having a multiplier 126, a transmitting mixer 128, a band pass filter 130 and a power amplifier (PA) 132. The IF signal processor 112 has a receiving IF processor 134, a frequency generator 138 and a transmitting IF processor 136.
In operation, a receiving signal of the frequency band of 800 MHz received through the antenna 114 is transmitted to the low-noise amplifier 118 through the demultiplexer 116. The receiving signal is low-noise amplified through the low-noise amplifier 118 and band pass filtered through the band pass filter 120 having a pass band of 868.5-893.5 MHz. The output of the band pass filter 120 is mixed with a local oscillating signal through the receiving mixer 122. The local oscillating signal is obtained by multiplying the frequency of an oscillating signal VCO generated from the frequency generator 138 of the IF signal processor 112 by one via a fundamental wave oscillating summing process performed in the multiplier 124. The oscillating signal VCO generated from the frequency generator 138 has an oscillating frequency f(VCO) of 953.88-978.88 MHz. The local oscillating signal generated from the multiplier 124 has the same frequency as the oscillating signal VCO generated from the frequency generator 138. Therefore, the receiving mixer 122 mixes the receiving signal having the frequency of 868.5-893.5 MHz with the local oscillating signal having the frequency of 953.88-978.88 MHz and generates an IF signal having the frequency of 85.38 MHz. The IF signal having the frequency of 85.38 MHz generated from the receiving mixer 122 is band pass filtered through a band pass filter 140 of the receiving IF processor 134 of the IF signal processor 112. The band pass filtered IF signal is gain-controlled through an automatic gain controller (AGC) 142. The gain-controlled IF signal is converted into an analog signal through a baseband signal converter 144 by a signal having the frequency of 170.76 MHz generated from the frequency generator 138 and then transmitted to a baseband signal processor.
The operation for transmitting a transmitting IF signal is performed in reverse order. A baseband signal converter 148 of the transmitting IF processor 136 converts a baseband analog signal received from the baseband signal processor into the transmitting IF signal by using a signal having the frequency of 19.68 MHz generated from the frequency generator 138 and a signal of the frequency of 260.76 MHz which the converter 148, itself, generates. The transmitting IF signal is gain-controlled through an automatic gain controller 146 and generated as an IF signal having the frequency of 130.38 MHz. The IF signal having the frequency of 130.38 MHz is transmitted to the transmitting mixer 128 of the digital/analog compatible converter 110. The transmitting mixer 128 mixes the IF signal having the frequency of 130.38 MHz with a local oscillating signal of the frequency of 953.88-978.88 MHz generated from the multiplier 126 and generates a transmitting signal having the frequency of 823.5-848.5 MHz. The local oscillating signal is generated through the same process as the local oscillating signal used in the receiving mixer 122 and will therefore not be described in detail herein. The transmitting signal is band pass filtered through the band pass filter 130 having the pass band of 823.5-848.5 MHz and power-amplified through the power amplifier 132. The power-amplified transmitting signal is transmitted to the duplexer 116 and radiated through the antenna 114.
As described above, the receiving and transmitting frequency ranges used in the digital/analog compatible portable telephone are 868.5-893.5 MHz and 823.5-848.5 MHz, respectively. However, the receiving and transmitting frequency ranges used in the PCS portable telephone are 1840-1870 MHz and 1750-1780 MHz, respectively. Since there is a great difference in the receiving and transmitting frequency ranges between the PCS portable telephone and the digital/analog compatible portable telephone, it is difficult to share the radio signal processing apparatus. That is, the frequency receiving and transmitting frequency ranges used in the PCS portable telephone are twice or more than the receiving and transmitting frequency ranges used in the digital/analog compatible portable telephone.
Accordingly, it would be highly desirable to provide a portable telephone having respective radio signal processing apparatus which can share the frequency band used in the digital/analog compatible mode and the PCS mode.